Control of diameter of ZnO nanorods grown by chemical vapor deposition with laser ablation of ZnO

• Published in: Superlattices and microstructures Vol. 42; no. 1; pp. 409 - 414
• Main Authors: Hirate, Takashi, Kimpara, Takashi, Nakamura, Shinichi, Satoh, Tomomasa
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.07.2007
• Subjects: Chemical vapor deposition; Laser ablation; Nanorod; Nanorod; Chemical vapor deposition; Laser ablation
• ISSN: 0749-6036; 1096-3677
• DOI: 10.1016/j.spmi.2007.04.011

We made a study of controlling diameters of well-aligned ZnO nanorods grown by low-pressure thermal chemical vapor deposition combined with laser ablation of a sintered ZnO target, which was developed by us. Until now, it has been impossible to control diameters of ZnO nanorods, while the growth orientation was maintained well-aligned. In this study we developed a multi-step growth method to fabricate well-aligned nanorods whose diameters could be controlled. Metal Zn vapor and O 2 are used as precursors to grow ZnO nanorods. N 2 is used as a carrier gas for the precursors. A substrate is an n -Si (111) wafer. A sintered ZnO target is placed near the substrate and ablated by a Nd–YAG pulsed laser during ZnO nanorod growth. The growth temperature is 530  ∘C and the pressure is 66.5 Pa. A vertical growth orientation of ZnO nanorods to the substrate is realized in the first-step growth although the diameter cannot be controlled in this step. When an O 2 flow rate is 1.5 sccm, well-aligned nanorods with 100 nm diameter are grown. Next, the second-step nanorods are grown on only the flat tip of the first-step nanorods. The diameters of the second-step nanorods can be controlled by adjusting the O 2 flow rate, and the growth direction is kept the same as that of the first-step nanorods. When the O 2 flow rate in second-step growth is smaller than 0.6 sccm, the diameter of the second-step nanorods is 30–50 nm. When the O 2 flow rate is between 0.75 and 3.0 sccm, the diameter is almost same as that of the first-step nanorods. When the O 2 flow rate is larger than 4.5 sccm, the diameter is increased with increasing O 2 flow rate. Further, the third-step ZnO nanorods with gradually increased diameters can be grown on the second-step nanorods with 1.5 sccm O 2 flow rate and without laser ablation.